1. Field of the Invention
The invention relates to a sintered material for a magnetic track brake, more particularly to an eddy current brake and/or magnetic track brake according to the preamble of claim 1, a magnetic track brake as well as a pole shoe for a magnetic track brake comprising such a sintered material.
2. Description of the Related Art
In magnetic track brakes according to the state of the art, preferably St37 steel was employed as friction material. What proved disadvantageous though in the use of a St37 friction layer was that build-up deposits occurred increasingly, which severely reduced the braking power of the brake. In order to restore the same, it was necessary to remove the build-up deposits by hand, which caused high maintenance costs. The employment of GGG40 spherulitic graphite iron did, it is true, result in fewer deposits forming, however, with friction layers of that type it was only possible to apply weak braking forces.
A further problem with magnetic track brakes according to the state of the art concerned the connection of the friction material to the carrier member or the basic member according to the state of the art, this connection is established by sintering, bonding or by welding. While the sintered connection broke open frequently already when weak shearing forces were applied, the bonded connections were subject to the disadvantage that they called for intermediate layers, in whose transition areas to the friction material block, crack formations and/or corrosions occurred so that an underfilm corrosion of the friction material block may take place gradually at one side which could lead to an impairment of the braking effect andxe2x80x94in an extreme casexe2x80x94to a failure of the brake lining. The bonding of the friction material to the carrier or supporting plate does, when manufacturing the brake lining by the thermal treatment of the bonding material, also calls for relatively long application times, which result in low production figures. A shortening of the application times of the thermal treatment of the bonding material is only possible by accepting an inadequate adhesive connection. Often the roughness of the surfaces to be bonded is also insufficient for making an adequate adhesion possible. That is why it has already been proposed in the DE-U1-B2 01 404, to provide the carrier plate on the side carrying the friction material block with a sinter-fused mounting bed of individual form-fitting shaped members with undercuts, recesses or suchlike, upon which the pressed-on friction material in the form of blocks is attached while filling in the undercuts, recesses or the like of the individual shaped members. However, in practical operation it has been shown that the adhesion continues to be inadequate since mechanical forces as well as occurring vibrations lead to a breaking up of the connection. The microscopically small shaped members forming a rough surface area are moreover comprised of a material other than the remaining mounting bed material, for which reason, by and large, a bed of homogeneous composition is formed, which, when subjected to loads or forces, tends to form cracks or to break apart. To this is added the circumstance that, on the connection point with a mounting bed, in lieu of one connection surface, two connection surfaces have to be provided, viz. the area of transition from the friction material body to the mounting bed and from the mounting bed to the carrier member.
From the EP-A-0 581 988, a brake block and a method for its fabrication as well as a magnetic track brake for road and rail vehicles, more particularly also for rail vehicles traveling at high or higher speeds is known. In order to render the connection of a carrier member on a friction material block for a brake block for road and rail vehicles safer, it is proposed here that the block of friction material be non- positively and/or form-fittingly embraced on several adjacent surface area portions not located in one plane by parts of the cast carrier member. This is achieved in that the finished sintered member is placed in a casting mold and the carrier member material is cast around the same. The brake block according to the EP-A-0 581 988 is characterized in that at least the friction material block is non-positively and form-fittingly encompassed on several adjacent surface area portions not located in one plane by parts of the cast carrier member. Thus not merely a connection of two adjoining, possibly roughened, surface areas is provided, but a connection which embraces the friction material block on the lateral surface portions or on all sides. The geometrically simplest connection, by way of example, resides in that the square brake block, on one of its front surfaces and on the lateral surfaces adjacent hereto, is embraced in its entirety or in part by the cast carrier member. In such a case, the lateral embracing pieces serve as supporting areas for the absorption of shearing forces or, by way of amplification, it is in this case also proposed to provide the friction material block and the cast carrier member on one front surface and/or on two oppositely located lateral surfaces with contourings in the form of elongated protuberances which, appropriately configured, intermesh and provide a natural positive locking of the cast carrier member around the friction material block.
It is the technical problem of the present invention to state a friction material for a magnetic track brake which is distinguished by a negligible tendency to forming buildxe2x80x94up deposits as well as a track brake or a pole shoe for a magnetic track brake, which permits adequate application times and with which sufficiently powerful braking forces are generated.
This technical problem is resolved by means of a sintered material according to the claim 1 as well as by a magnetic track brake having a magnetic flux-carrying area and/or a magnetic flux-separating area, at least in part, in the form of a friction material that is a sintered material comprising a proportion of pulverized wear inhibitor and/or a proportion of powder forming a protective layer, in which case the invention also includes a pole shoe for a magnetic track brake according to claim 43. The invention consequently consists in that a sintered material is made available as friction material for a pole shoe, a pole shoe area or pole shoe friction areas for a magnetic track brake comprising at least
a proportion of pulverized wear inhibitor and/or
a proportion of powder forming a protective layer.
As pulverized wear inhibitor, by preference one or combinations of several of the following substances are employed: Al2O3, ZrO2, Al2TiO5, Y2O3, SiC, Si3N4, WC, Cr3C2, TiC.
The powder forming the protective layer is preferably selected from one of the following substances: Spherulitic graphic iron, graphite, iron sulfide, manganese sulfide, lead, molybdenum sulfite.
In a preferred embodiment, the sintered material may also possess a proportion of magnetically conductive powder, by way of example, iron powder.
A particularly wear-resistant composition of the sinter material as friction material is:
If the sintered material in its first embodiment comprises 80% to 99% of a magnetically conductive material, in that case the same possesses a proportion of iron. If the sintered material comprises a magnetically non-conductive material, then the same possesses preferably several or combinations of the following substances:
tin, copper, zinc, nickel, aluminum or alloys of these substances, by way of example, bronze, brass, nickel silver.
According to a further aspect of the invention, it is intended to provide a low-maintenance track brake, in which no build-up deposits occur or merely in a very thin and small form, i.e. negligible deposits and which, over and above that, allows application times that are approximately comparable with the previous steel members. The braking power is identical with or superior to that of the track brakes with steel members employed up to now.
The pole shoe area carrying magnetic flux of a track brake has to meet the following prerequisites:
Generation of the magnetic power of attraction (adhesive power),
Perform friction work (braking)xe2x80x94without the occurrence of build-up deposits.
Both these preconditions are met when a magnetic track brake of the type in question comprises a sintered material according to the invention, in which connection it was surprising that it did prove possible to meet the prerequisites and to achieve the advantages with the composition stated in the foregoing. A pole shoe area carrying a magnetic flux of this composition assumes both tasks, viz. to generate a magnetic adhesive power and to perform friction work.
Further constructions of the invention are described in the subclaims.
Apart from the application of the sintered material in the form of a coating, the sintered material may also be executed in the form of a compact block of friction material which is secured on the basic and/or carrier member.
In a first embodiment, the carrier member can be cast and, at the connection point to the friction material block, may possess on at least two oppositely located sides, elongated ribs or protuberances each with undercuts, which engage non-positively and form-fittingly into pertinently adapted grooves or recesses on the block of friction material. A special embodiment of such a non-positive and form-fitting connection is a dovetailed accommodation space as is known in e.g. guideways. In this case, the friction material block, preferably on its rear, in the form of a broad rib with undercuts on both sides, is provided with the positive dovetail, while the carrier member possesses an appropriately adapted negative recess. The rib in question or different protuberances with undercuts are formed already in the course of the fabrication of the friction material block along with the latter so that the rib, together with the remaining friction material block, forms a homogeneous shaped member. Since the carrier member with its contouring reaches into the undercuts, in which case also the carrier member constitutes a material-specific part, already by the construction of the external contour, a breaking up of the connection point is very largely ruled out.
According to a further embodiment of the invention, the ribs or protuberances on the one hand and the pertinently configured grooves or recesses on the other are provided on all sides of the carrier member or block of friction material are provided while in each case interlocking.
As already mentioned, according to a special embodiment of the friction material member, on the connection area facing away from the active brake surface and the lateral surfaces adjoining hereon, is embraced by the carrier member across a predetermined height, in which case the lateral surfaces can be constructed so as to be smooth or likewise provided with a contouring in the form of a rib with undercuts. By preference, the carrier member and the friction material block terminate flush with each other on the sides or on the front surface.
As material for the friction material block, inter alia also a sintered material and/or the carrier member, grey cast iron, spherulitic graphite iron or cast steel are employed, in which case the sintered material possesses the material composition stated in the claims 1 to 7.
From an aspect of process engineering, a connection between the friction material block and the basic or carrier member can be established in that the block of friction material, in a powder-metallurgical manner, after the finishing sintering, is subsequently placed in a casting mold and is completely or in part cast around so that a non-positive and/or form-fitting connection of the thusly cast carrier member to the block of friction material is created. The contouring configurations or the macro serratio or denticulation in the form of ribs or other protuberances with undercuts or also grooves or recesses are incorporated prior to the sintering, during the sintering or subsequent to the sintering in to the friction material block. By the casting of the block of friction material immersed in the cast material, the carrier member is joined form-fittingly within the region of the immersion depth with the contour of the friction material block so that, after the cooling, a rigid connection exists between the friction material block and the carrier member.
By preference, the casting temperature is selected so high that the casting material diffuses into the marginal zones of the friction material block, e.g. up to 20 urn, so as to obtain in this zone an atomic diffusion bond. Hereby the form fitting is improved further. The advantage of the aforedescribed process consists in that it is possible to rationalize the fabrication further since the otherwise necessary sintering for securing the friction material block to a carrier plate or to the basic or carrier member is dispensed with just like the roughening of the connection areas, the insertion and pretreatment of intermediate layers and the application of possible connecting means, such as adhesives or solder.
The pole shoe areas separating the magnetic flux may, on the underside forming the friction surface, be provided with a thin, extremely wear-resistant, antimagnetic coating comprising the sintered material according to the invention, which is shockproof and temperature-stable and which prevents the formation of build-up deposits. It is also possible for each pole shoe to be comprised of different materials and areas, of which one area assumes the generation of the magnetic adhesive power and the other area takes over the performance of the friction work.